1. Field of the Invention
The present invention relates to a water vapor permeable, waterproof fabric. More particularly, the present invention relates to a water vapor-permeable, waterproof fabric which has a coating layer formed on a substrate fabric and comprising thermoplastic polyetherester elastomers and exhibits an excellent water vapor permeability and a high resistance to water permeation therethrough.
2. Description of the Related Arts
When a fabric is worn as clothing on the human body, the clothing is required to exhibit both of a high water vapor permeability to allow a water vapor derived from perspiration generated from the human body to leave through the clothing and a high resistance to permeation of water, for example, rain, through the clothing, to prevent penetration of water into the clothing.
As means for satisfying the above-mentioned two requirements, it is known that one side surface of a substrate consisting of a fiber fabric can be laminated with a film comprising a polytetrafluoroethylene or a polyurethane elastomer, or can be coated with a polyurethane elastomer.
The conventional water vapor permeable, waterproof fabrics produced as mentioned above are environmentally disadvantageous in that when these fabrics are discarded and burnt, the laminated or coated polymers cause gasses harmful for the human body to generate.
Accordingly, the polymer materials for the water vapor-permeable, waterproof fabrics which have both a high water vapor permeability and an excellent waterproof property and cause no or little affect on the environment, are in strong demand.
For this demand, it is expected that the above-mentioned polytetrafluoroethylene and polyurethane elastomers will be replaced by polyetherester elastomers (PEE) which have excellent heat resistance and mechanical properties, are capable of forming films having a moderate elasticity and a good hand, and can be burnt without generating harmful combustion gases.
As a water vapor-permeable, waterproof fabric using the above-mentioned PEE, U.S. Pat. No. 4,493,870 discloses a laminated fabric comprising a film formed from a PEE resin in which at least 70% by weight of polyalkylene glycol (PAG) for forming long chain-formed ester segments have an atomic ratio of carbon atoms to oxygen atoms contained in the molecular chains of 2.0 to 2.4, laminated on a surface of a substrate fabric. The U.S. patent states that the moisture-permeable waterproof fabric exhibits excellent moisture permeability and resistance to water permeation therethrough and is free from environmental problems. The inventors of the present invention studied the water vapor-permeable waterproof fabric of the U.S. patent, and found that the PEE film is fixed to the substrate fabric through an adhesive agent, and when a polyurethane resin is used as an adhesive agent, and the resultant laminated fabric is discarded and burnt, the polyurethane resin contained in the laminated fabric, even in a small amount, causes generation of a poisonous gas. Also, the inventors of the present invention found that, in the production of the laminated fabric of the U.S. patent, the PEE resin must be formed into a film before laminating procedure, and the film-formation procedure causes the cost of the laminated fabric production to be high in composition with that produced by the coating procedure. Namely, the disadvantages of the water vapor-permeable, waterproof fabric of the U.S. patent as mentioned above are inherent to the fabric produced by the lamination method.
Also, it was found that when the PEE resin layer as mentioned above is formed by the coating layer, since the 70 weight % or more of the PAG from which long chain ester segments are formed are ones having an atomic ratio of carbon atoms to oxygen atoms contained in the molecular chains of 2.0 to 2.4, the PEE resin is difficult to form into a coating layer on the substrate fabric surface with a uniform thickness over the entire surface of the fabric, while the resultant PEE coating layer exhibits a high water vapor-permeability. The above-mentioned difficulty is inherent to the PEE resin per se.
The problems on the coating layer will be further discussed in detail below.
The water vapor-permeability of the PEE resin is derived from the PAG moieties contained in the molecular chain structures of the PEE and having a high hydrophilicity. Thus, the higher the content of moieties derived from polyethylene glycol which has a higher hydrophilicity than that of other polyalkylene glycols in the coated PEE layer, the higher the water vapor permeability of the coated PEE layer. However, the PEE resin having a high content of the polyethylene glycol moieties is disadvantageous in that when the coating liquid containing the PEE is coated on the substrate fabric, the coating liquid easily penetrates into the inside of the substrate fabric. Namely, in the resultant coated fabric, the resultant surface-coating layer of the PEE resin has a small thickness in view of the total amount of the PEE resin applied to the surface of the substrate fabric, and is disadvantageous in that the thickness of the surface coating layer is uneven in response to ununiform penetration of the coating liquid into the inside of the substrate fabric. Therefore, the resultant coated fabric exhibited a significantly poorer waterproofness than that of the PEE film-laminated, water vapor-permeable, waterproof fabric of the U.S. patent.
Namely, when the PEE layer of the U.S. patent is formed on the substrate fabric surface by the coating method in place of the laminating method disclosed in the U.S. patent, the coating liquid for the PEE layer cannot coat the substrate fabric surface with uniform thickness, and thus the resultant coated PEE layer is uneven in the thickness thereof and thus exhibits a poor resistance to water penetration because water can easily penetrate into the substrate fabric through thin portions of the coated PEE layer.
The resistance to water penetration of the coated PEE layer can be enhanced by increasing the average thickness thereof. The increase in the average thickness causes the resultant PEE-coated fabric to exhibit a reduced softness and poor water vapor-permeability.
Also, the inventors of the present invention further found that the PEE film-laminated, water vapor-permeable, waterproof fabric the U.S. patent is unsatisfactory in wear resistance thereof and thus the wear resistance should be improved.
Accordingly, the PEE-coated fabric having a coated PEE layer with a uniform thickness and exhibiting both a satisfactory water vapor permeability and a sufficient resistance to water permeation, is not yet practically available.
An object of the present invention is to provide a water vapor-permeable waterproof fabric having a composite coating layer comprising polyetherester elastomers and formed on a substrate fabric, and exhibiting a satisfactory softness, a sufficient water vapor-permeability and an excellent resistance to water (hydraulic) pressure, and a process for producing the same while solving a problem such that a coating liquid containing the polyetherester elastomer easily penetrates into the inside of the substrate fabric. Another object of the present invention is to provide a water vapor-permeable waterproof fabric having a high wear resistance in addition to the satisfactory softness, sufficient water vapor-permeability and excellent water pressure resistance, and a process for producing the same.
The above-mentioned objects can be attained by the water vapor-permeable waterproof fabric and the process for producing the same, of the present invention.
The water vapor-permeable waterproof fabric of the present invention comprises:
a substrate fabric comprising a fiber material; and
a composite coating layer formed at least a portion of the surfaces of the substrate fabric and containing (A) a lower layer directly bounded to the substrate fabric and (B) an upper layer formed on the lower layer,
wherein the lower and upper layers (A) and (B) comprise one of two polyetherester elastomers (PEE) different in coating layer-forming property from each other, and each comprising polyalkylene glycol (PAG) residues, alkylene glycol (AG) residues and dicarboxylic acid (DC) residues, and satisfy the following requirements:
(a) in the polyetherester elastomer (PEEA) for the lower layer (A), the polyalkylene glycol (PAG), residues contain polytetramethylene glycol residues in a content of 90% by weight or more;
(b) in the polyetherester elastomer (PEEB) for the upper layer (B), the polyalkylene glycol (PAG): residues contain polyethylene glycol residues in a content of 50% by weight or more;
(c) the thickness of the composite coating layer is in the range of from 5 to 50 xcexcm; and
(d) the lower layer (A) is in an amount of 5 to 40% by weight based on the total weight of the composite coating layer including the lower and upper layers (A) and (B).
The process of the present invention for producing a water vapor-permeable waterproof fabric comprises coating at least a portion of the surfaces of a substrate fabric comprising a fiber material with a composite coating layer comprising (A) a lower layer and (B) an upper layer,
wherein the lower layer (A) is formed on and bonded directly to at least a portion of the surfaces of substrate fabric, and the upper layer (B) is formed on and bonded to the lower layer (A), and
the lower and upper layers (A) and (B) comprise one of two polyetherester elastomers (PEE) different in coating layer-forming property from each other, and each comprising polyalkylene glycol (PAG) residues, alkylene glycol (AG) residues and dicarboxylic acid (DC) residues, and satisfy the following requirements;
(a) in the polyetherester elastomer (PEEA) for the lower layer (A), the polyalkylene glycol (PAG) residues contain polytetramethylene glycol residues in a content of 90% by weight or more;
(b) in the polyetherester elastomer (PEEA) for the upper layer (B), the polyalkylene glycol (PAG) residues contain polyethylene glycol residues in a content of 50% by weight or more;
(c) the thickness of the composite coating layer is in the range of from 5 to 50 xcexcm; and
(d) the lower layer (A) is in an amount of 5 to 40% by weight based on the total weight of the composite coating layer including the lower and upper layers (A) and (B).